It has become commonplace in the oil and gas industry to use coiled tubing in downhole intervention in oil and gas wells. Coiled tubing typically ranges in diameter from 1 to 4.5″, and is stored on large spools located near the wellhead.
Coiled tubing serves multiple purposes in the oil and gas industry, such as: fluids can be delivered downhole for various stimulation and maintenance operations (including fluids entrained with particulate proppant), production fluids can be pumped out of the wellbore and recovered for refinement, and wellbore tools (also known as a tool string) can be lowered downhole while suspended from the coiled tubing as coiled tubing is typically manufactured out of high tensile strength materials such as steel. In some applications, these suspended wellbore tools can be hydraulically powered by pressurized fluid provided by the coiled tubing.
Previously, wireline technology was used to lower tools (such as logging instruments, mud drills, perforation apparatuses, etc.) downhole into the wellbore under the force of gravity. Wirelines are typically only suitable for use in perfectly vertical wellbores due to the fact that wirelines are inherently flexible and cannot be “pushed” into a wellbore.
One advantage presented by the use of coiled tubing is that due to the rigid (yet limitedly flexible) nature of the tubing, it can be pushed into the wellbore and therefore can be used in wellbores that deviate from a perfectly vertical alignment. In this way, coiled tubing can be used in directional drilling applications that are wholly unsuited to predecessor wireline technology.
Coiled tubing is “pushed” into or “pulled” from the wellbore by way of a coiled tubing injector. Typical coiled tubing injectors consist of a pair of opposed “endless” (i.e. continuously looped) chainsets that rotate in the same plane. These opposed chainsets each have a number of gripper assemblies which forcibly grip the coiled tubing. Each chain set has a bearing skate which pushes the two chainsets together, thereby squeezing the coiled tubing in the opposed gripper assemblies. In this way, the coiled tubing is “pulled” off the spool and “pushed” into the wellbore by the coiled tube injector.
U.S. Pat. No. 6,609,566 discloses a coiled tubing injector head having multiple endless chains and a plurality of gripper assemblies are positioned around the middle links of the endless chains.
U.S. Pat. No. 5,188,174 discloses a coiled tubing injector having a frame upon which is mounted a pair of opposed endless flexible conveyor members. The conveyor members have opposed elongated parallel runs spaced apart to form a path for engagement with the tubing by gripper blocks disposed on the conveyor members.
CA2236358 discloses a gripping element of a coiled tubing injector that has a carrier and a removable gripping shoe mounted to the carrier. The removable shoe slides onto slots formed on the carrier and is floated on the carrier by inserting an elastomeric pad sandwiched between the carrier and shoe.
CA 2699906 discloses a gripper for use within a coiled tubing injector unit and having a carrier for securing the gripper to the chain drive mechanism of the coiled tubing injector unit and a gripping shoe carried by the carrier.
However, previously known gripper assemblies are often inflexible and can place undue stress on the components of the coiled tubing injector, particularly load supporting bearings. This is exacerbated by the fact that many oil and gas wells are located in extremely hostile environments that increase the maintenance requirements of oilfield production equipment and specifically equipment with moving parts.
Therefore, an improved gripper assembly is needed to reduce maintenance costs and extend operating life of the components of the presently available coiled injectors.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.